1. Field of the Invention
The present invention relates to a slider member having micro-protrusions for reducing the sliding friction and a method of forming such micro-protrusions on the substrate surfaces, for example, between a magnetic disc and a slider of the magnetic head.
2. Description of the Related Art
Reading and writing on magnetic memories are performed by the relative sliding of a slider of a magnetic head sliding against a magnetic disc (hard disc). A dynamic pressure (wind pressure) is generated by the relative motion of the sliding surfaces, and forces the slider to separate from the disc surface; however, to obtain high strength signals, it is desired that the separation force be overcome and the distance between the slider and disc surfaces be minimized. In order to satisfy this condition even at low relative speeds without crashing the slider against the disc, the two surfaces may be made planar; however, when such two planar surfaces are brought close together, sticking (adherence) is generated because of the presence of moisture in the ambient air. Also, if a lubricant is used to reduce the friction, the phenomenon of sticking becomes even more aggravated. Sticking becomes more severe as the surface roughness (height of protrusions) diminishes, as the humidity increases and as the lubricant thickness increases. Therefore, to satisfy the above requirements in the presence of humidity and lubricant, the surfaces should be sufficiently smooth to minimize the distance between the slider and disc surfaces while sufficiently rough to prevent sticking. To meet such contradictory requirements, it has been a practice to provide micro-protrusions of the order of 10 nanometers (nm) on the sliding surfaces. This will be explained further with reference to FIG. 20.
FIG. 20 is a cross sectional view of micro-protrusions formed on a sliding surface by a conventional technique. In FIG. 20, the reference numeral 1 refers to a substrate of the magnetic disc made of an aluminum alloy, which may be covered with a nickel plating, or a glass substrate. The substrate 1 is first made into a plain surface 2a, then the surface 2a is abraded lightly with abrading tape or cloth containing powder particles so as to produce a roughened surface containing micro-protrusions 2a1, 2a2, 2a3, of the order of 10 nm height. On top of the irregular shaped surface thus formed, a magnetic film layer and and protective film layer, made of a carbon film, SiO2 film, ceramic film or other type of protective films, are deposited in succession to ultimately produce a sliding surface so that the contour of the outermost protective surface reproduces the irregular surface structure of the substrate.
FIG. 21 is a cross sectional view of micro-protrusions on a sliding surface produced by another conventional technique. In this figure, as in FIG. 20, the reference numeral 1 refers to a substrate of a magnetic disc. As in the previous case, the surface of the substrate 1 is made as a plain surface 2b, and is then processed by such processes as sputtering and vapor deposition to form numerous protrusions 2b1, 2b2, and 2b3, on the top surface 2b. This step is followed, as before, by deposition of a magnetic film layer and a protective film layer to ultimately produce a sliding surface having micro-protrusions. In this case, the top surface 2b may not necessary be a surface of the substrate, and may be a flat surface of a magnetic film or a protective film to which similar deposition techniques can be applied to ultimately produce a protective film layer having micro-protrusions 2b1, 2b2, and 2b3, to be used as the sliding surface.
FIG. 22 is a cross sectional view of micro-protrusions, on a sliding surface made by yet another conventional technique. The reference numeral 1 refers again to a substrate of a magnetic disc as in the case shown in FIG. 20. As in the previous case, the surf ace is first made as a plain surface 2c, then, depressions are produced by a dry etching or wet etching, thereby producing a top surface 2c having numerous protrusions 2c1, 2c2, and 2c3. This step is followed, as before, by deposition of a magnetic layer and a protective layer, to ultimately produce a protective top sliding layer having an irregular surface structure. In this case also, the top surface 2c may not necessary be a surface of the substrate, and may be a flat surface of a magnetic film or a protective film to which similar deposition techniques can be applied to ultimately produce a protective film layer having micro-protrusions 2c1, 2c2, and 2c3 to be used as the sliding surface.
There has been a serious problem in the actual use of the magnetic discs produced by the techniques described above. It has been found that, during the use of the magnetic disc in sliding contact with the slider of a magnetic head, foreign particles such as debris due to wearing as a result of the sliding action are entrapped between the slider and the disc, and are outstretched so as to stick to the slider or the disc thereby resulting in impeded transmission of signals. Furthermore, because moisture and lubricant may not be distributed uniformly across the surface of the disc, local sticking can occur between the slider and the disc, thereby causing abnormally high friction or, in some cases, self-vibration of the head (referred to as stick-slip), caused by sudden release from sticking, can result in plastic deformation or irregular friction phenomenon.
The debris biting and sticking phenomenon related to the conventional devices were examined in detail by the present inventors that led to the following observations. The primary causes are that, in the conventional devices, the inclusive angle of contact of the upright surface (side surface) of the micro-protrusions opposing the direction of relative movement of the sliding surface is small, which promotes the formation of a large meniscus. The formation of a meniscus on each of the various shaped of micro-protrusions will be explained in more detail with reference to FIGS. 23A, 23B and 23C which correspond to meniscus formation on micro-protrusions, 2a1, 2b1, and 2c1, having profiles show in FIGS. 20, 21 and 22, respectively. In FIGS. 23Axcx9c23C, the slider surface 3 (on a magnetic head for example) is in contact with a liquid substance 4 (moisture in air or lubricant) and the magnetic disc moves in the direction D relative to the slider surface 3- The meniscus means a curved boundary surface having a radius of curvature R formed between the air phase and the liquid phase. The relationship between the radius R and the profile shape of the micro-protrusions will be discussed further with reference to FIG. 24.
FIG. 24 is a cross sectional view of a micro-protrusion. As a representative profile of a micro-protrusion, the profile of the protrusion 2c, shown in FIG. 23C has been chosen; however, this discussion applies in general to other profiles of micro-protrusions. The reference numerals are the same as those used earlier. A foreign debris particle 5 is present in the fore direction. In this example, the distance between the slider surface 3 and the bottom surface of the protrusion 2c1 is shown to be about 10 nm (the height of the micro-protrusion), and the profile is assumed to be symmetrical. The angle of the meniscus is xcex8 which refers to the inclusive angle of contact between the slider surface 3 and the leading surface in the moving direction of the micro-protrusion 2c1. Force F1 is exerted to the micro-protrusion 2c1, by the liquid substance 4.
If the inclusive angle xcex8 is small, there is a larger area of contact between the slider surface 3 and the micro-protrusion 2c1, and the meniscus, i.e. a radius of curvature R, becomes large. The larger the meniscus, the larger the force F1 to cause more sticking. Furthermore, it can be seen that if the inclusive angle xcex8 is small, it is more likely that the debris particle can become lodged in the wedge shaped interface between the slider surface 3 and the micro-protrusion 2c1. It has therefore been concluded that debris biting and sticking phenomena are both related fundamentally to the inclusive angle of contact xcex8 between the sliding surface and the micro-protrusion.
When the micro-protrusions produced by the conventional techniques shown in FIGS. 20xcx9c22 were examined, it became apparent that the inclusive angle xcex8 is small (less than 70 degrees) and inevitably, large menisci are formed. In the conventional approach, the effort had been focused on the production aspects of micro-protrusions, and no attention has been paid to the shape of the micro-protrusions or the importance of the meniscus in causing operational problems.
It is an object of the present invention to resolve the problems inherent in the conventional techniques of producing micro-protrusions by emphasizing the importance of the structure of the micro-protrusions and a process of making optimum structures for micro-protrusions on the sliding surfaces. The approach is to prevent the phenomenon of sticking and reduce entrapping of foreign particles between the sliding surfaces.
This object has been achieved in a method for making micro-protrusions or micro-cavities on the surface of a substrate comprising the steps of: placing the substrate in a process chamber; supporting a mask member, having a micro shielding surface, independent of and in front of the substrate; and irradiating fast atomic beams onto the surface of the substrate through the mask member. Here, it is preferable that the micro-protrusions or micro-cavities have a height or depth ranging from 10 to 50 nm, and, for use in a slider member, 10 to 1,000,000 protrusions or cavities are formed on a 1 mm2 surface of the substrate.
The mask member having a micro shielding surface has a very small area of projection for shielding the fast atom beams so as to form micro-sized unetched surfaces in a form of micro-protrusions. The mask member is constructed mechanically or physically independent of the substrate, and thus is separable from the substrate and is not integral with the substrate, as would be a photoresist layer coated on the substrate surface. The mask member is usually held in parallel to the substrate surface.
The substrate may be a slider member for use in a mechanically sliding portion, that is, at least one of the members relatively movable to the other in a sliding manner. The fast atomic beams are usually irradiated substantially at right angles onto the surface of the substrate.
The mask member may comprise micro-objects dispersed on the surface of the substrate, e.g. round shaped micro-powders, strings, rods, debris or in any shape. The micro-objects may comprise at least one material selected from the group comprising alumina, carbon, Si3N4, SiC, TiN, ZrO2, MgO, and synthetic resin. Toner particles for use in copying machines are also usable.
The mask member may comprise a plurality of fine wire or rod members disposed in contact with or in proximity of the substrate surface, which are usually arranged in parallel or to form a matrix.
Another aspect of the invention is a method for making micro-protrusions or micro-cavities on a surface of a substrate comprising the steps of: dispersing micro-particles on the substrate surface; and irradiating the substrate surface with fast atomic beams at an angle of incidence determinable by an inclined angle measured with respect to a rotation axis normal to the substrate surface while a beam source relatively swivels about the rotation axis. The inclined angle with respect to the rotation axis is more than 0 degree and can be selected in a range from 0 to 90 degrees. Usually the beam source is driven to swivel about the rotation axis, however, the substrate can be driven to rotate about the beam axis to obtain the same effect.
Another aspect of the invention is a method for making micro-protrusions or micro-cavities on a surface of a substrate comprising the steps of dispersing micro-particles susceptible to etching by fast atomic beams on the substrate surface; and irradiating the substrate surface with fast atomic beams at an angle of incidence determinable by an inclined angle measured with respect to a rotation axis normal to the substrate surface while a beam source relatively swirls about the rotation axis.
Another aspect of the invention is a method for making micro-protrusions or micro-cavities on a surface of a substrate comprising the steps of a first irradiation step irradiating the substrate surface with fast atomic beams through a mask member consisting of parallel wire or rod members disposed in contact with or in proximity to the substrate surface; and a second irradiation step irradiating the substrate surface with fast atomic beams through a mask member consisting of parallel wire or rod members disposed in contact with or in proximity to the substrate surface, the parallel wire or rod members being oriented at right angles or at an oblique angle to those in the first irradiation step.
Another aspect of the invention is a slider member formed with a plurality of micro-protrusions or micro-cavities on at least one surface thereof, wherein the micro-protrusions or micro-cavities comprise top or bottom surfaces and side surfaces, and an inclusive angle of side surfaces of the micro-protrusions or micro-cavities is selected within a range of angles between 80 to 110 degrees measured with respect to the relative sliding direction of the slider member which is usually a direction parallel to the slider surface.
According to this aspect of the present invention, because the inclusive angle of contact of the side surfaces (upright surfaces) is selected within a range of angles between 80 to 110 degrees, foreign particles do not become entrapped between the micro-protrusion and the sliding surface, but are simply transported by being abutting against the micro-protrusions. In effect, the depression spaces formed by the protrusions act as pockets for the debris particles. Because of the appropriate choice of the inclusive angle, the size of the meniscus is reduced compared with the meniscus size formed in association with conventional micro-protrusions, and sticking is prevented without changing the usual operating parameters such as protrusion height, volume or lubricant thickness or temperature of operation. In other words, another parameter for preventing sticking has been found to assure more reliable operation. Therefore, by forming the inclusive angle of contact to be between 80 to 110 degrees, a thicker layer of lubricant can be used to reduce wear while prevent sticking. Conversely, the control of the meniscus size, by controlling the inclusive angle of contact, enables the force of separation due to the presence of air pressure between the sliding surfaces and the force of attraction working at the meniscus to be optimally balanced, thereby leading to a possibility of effective adjustment of separation distance of the order of nanometers.
The friction reduction effect of the protrusion is especially high when the inclusive angle is larger than 90 degree, i.e. when 90 less than xcex8xe2x89xa6110, because when a wear particle hits the protrusion, it goes down along the upright surface (side surface) so as to not cause generation of large friction. The advantage is particularly prominent when the depression is formed as a lattice configuration. Otherwise, a large friction is generated to cause damage to the slider member, fluctuation of the attitude of the slider member, distortion of the support mechanism for the slider member, or deterioration of the sliding surface, which may, at the worst, make the slider unusable.
The above and other objects, features, and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings which illustrate preferred embodiments of the present invention by way of example.